Product gas concentrator utilizing vacuum swing adsorption and method associated therewith

ABSTRACT

Systems and methods associated with providing a concentrated product gas utilizing a vacuum swing adsorption process are provided. In one embodiment, the system includes first and second sieve beds, a scavenger pump, and a controller. In one embodiment, the method includes: separating one or more adsorbable components from a source gaseous mixture via first and second sieve beds in alternating and opposing filling and purging cycles of a vacuum swing adsorption process to form the concentrated product gas and pressurizing the concentrated gas for delivery to a user. Other embodiments include selectively controlling a variable restrictor based at least in part on a desired output setting to selectively provide flow between the first and second sieve beds such that the flow for at least one output setting is different from the flow for at least one other output setting in relation to corresponding filling cycles.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to, and the benefits of, U.S. provisional application Ser. No. 61/750,517, filed on Jan. 9, 2013, which is incorporated by reference herein in full. This application is related to co-pending U.S. application Ser. No. 12/106,861, filed Apr. 21, 2008. The contents of all above-identified patent application(s) and patent(s) are fully incorporated herein by reference.

BACKGROUND

Various applications exist for the separation of gaseous mixtures. For example, the separation of nitrogen from atmospheric air can provide a highly concentrated source of oxygen. These various applications include the provision of elevated concentrations of oxygen for medical patients and flight personnel. Hence, it is desirable to provide systems that separate gaseous mixtures to provide a concentrated product gas, such as a breathing gas with a concentration of oxygen.

Several existing product gas or oxygen concentrators, for example, are disclosed in U.S. Pat. Nos. 4,449,990, 5,906,672, 5,917,135, 5,988,165, 7,455,717, 7,722,700, 7,875,105, 8,070,853, and 8,282,717, and U.S. Pat. Appl. Ser. Nos. 61/608,874, 61/661,260, and Ser. No. 13/790,312 which are commonly assigned to Invacare Corporation of Elyria, Ohio, and fully incorporated herein by reference.

DRAWINGS

FIG. 1 provides a perspective view of an exemplary embodiment of a product gas concentrator;

FIG. 2 provides an exploded view of the product gas concentrator of FIG. 1;

FIGS. 2A-D provide exploded views of other exemplary product gas concentrators;

FIGS. 3A-H provide various perspective, sectional, exploded views of an exemplary embodiment of a sieve bed and product tank assembly for an exemplary product gas concentrator;

FIGS. 3I-O provide various perspective, sectional, exploded views of an alternate exemplary embodiment of an end cap for the sieve bed and product tank assembly of FIG. 3A;

FIGS. 4A-D provide various perspective, sectional, exploded views of an exemplary embodiment of a vacuum pump assembly for an exemplary product gas concentrator;

FIG. 4E provides a top view of an alternate exemplary embodiment of a plurality of suspension links for the vacuum pump assembly of FIG. 4A;

FIG. 4F provides a perspective view of another exemplary embodiment of a vacuum pump assembly for an exemplary product gas concentrator;

FIG. 4G provides a block diagram of exemplary pressure stages in an exemplary embodiment of a product gas concentrator;

FIG. 5A provides a schematic block diagram of an exemplary embodiment of another product gas concentrator;

FIG. 5B provides a block diagram including an exemplary controller of an exemplary embodiment of another product gas concentrator;

FIG. 5C provides a schematic block diagram of an exemplary embodiment of another product gas concentrator;

FIG. 5D provides a timing diagram for an exemplary embodiment of a valve control scheme for the product gas concentrator of FIG. 5A;

FIG. 5E provides a block diagram showing several exemplary strategies for flow from sieve bed 1 to sieve bed 2 in an exemplary embodiment of an exemplary product gas concentrator;

FIG. 5F provides a block diagram showing several strategies for flow from sieve bed 2 to sieve bed 1 in an exemplary embodiment of an exemplary product gas concentrator;

FIG. 5G provides top and side views of an exemplary embodiment of a valve assembly for the product gas concentrator of FIG. 5A;

FIG. 5H provides a block diagram of the valve assembly of FIG. 5G;

FIGS. 6A and 6B provide perspective and sectional views of an exemplary embodiment of an output port for an exemplary product gas concentrator;

FIG. 7 provides a flow chart of an exemplary embodiment of a process for calibrating in relation to an exemplary vacuum/pressure sensor in an exemplary product gas concentrator;

FIG. 8 provides a flow chart of an exemplary embodiment of a process for determining a time duration for dispensing a bolus of concentrated product gas in an exemplary product gas concentrator;

FIG. 9 provides a timing diagram for an exemplary embodiment of a conserver valve control scheme for an exemplary product gas concentrator;

FIG. 10 provides a block diagram of still another exemplary embodiment of a product gas concentrator; and

FIG. 11 provides a flow chart of an exemplary embodiment of a process for dispensing a concentrated product gas to a user in conjunction with a product gas concentrator.

DESCRIPTION

Illustrated in FIG. 1 is one embodiment of an exemplary oxygen concentrator 100. Oxygen concentrator 100 includes a housing 102 having a front portion 104 and a rear portion 106. Front and rear portions 104 and 106 include a plurality of openings for the intake and discharge of various gases such as, for example, the intake of room air and the discharge of nitrogen and other gases. Oxygen concentrator 100 generally intakes room air, which is mostly comprised of oxygen and nitrogen, and separates the nitrogen from the oxygen. The oxygen may be stored in a storage tank and the nitrogen may be discharged back into the room air. For example, the oxygen gas may be discharged through port 108 to a patient through tubing and nasal cannula.

FIG. 2 is an exploded perspective view of the exemplary oxygen concentrator 100 of FIG. 1. Oxygen concentrator 100 further includes a central frame 202 having a circuit board and other exemplary components connected thereto. These components include a battery pack 204, sieve bed and product tank assemblies 206 and 208, accumulator 209, vacuum pump 210, scavenger pump 211, cooling fan 212, and valve assembly 214. While these components are described as being connected to central frame 202 that need not be the case. One or more of these components may be connected to housing portions 104 or 106. Other exemplary components are also housed within oxygen concentrator 100 including, for example, sound attenuators or mufflers 216 and 218 and one or more inlet filters 220. In other embodiments, the sound attenuators or mufflers may be integrated into the sieve bed bottom caps.

In addition, several other embodiments of the invention include various combinations of the above components. For example, some of these embodiments are shown in FIGS. 2A-2D as follows: FIG. 2A shows an embodiment without accumulator 209, with one sieve bed and product tank assembly 206, and with one sieve bed and accumulator assembly 208′; FIG. 2B shows an embodiment without scavenger pump 211 and with combination vacuum/scavenger pump assembly 210′; FIG. 2C shows an embodiment without accumulator 209, without scavenger pump 211, with one sieve bed and product tank assembly 206, with one sieve bed and accumulator assembly 208′, and with combination vacuum/scavenger pump assembly 210′; and FIG. 2D shows an embodiment without cooling fan 212. As can be appreciated, many other embodiments including other combinations of these components can be utilized to practice the invention.

Sieve Bed and Product Tank Assembly

Referring now to FIGS. 3A and 3B, and more particularly to the perspective view FIG. 3A, sieve bed and product tank assembly 206 is shown. Sieve bed and product tank assembly 208 is similarly configured and will not be described separately. Assembly 206 includes a body having a sieve bed portion 300 and a product tank portion 302. The distal ends of the body have first and second end caps 304 and 306. End cap 304 includes outlets, such as, outlet ports 308 and 310. Outlet port 308 is associated with the sieve bed portion 300 and outlet port 310 is associated with the product tank portion 302. End cap 306 includes inlets, such as input ports 312 and 314. Input port 312 is associated with sieve bed portion 300 and input port 314 is associated with product tank portion 302. End caps 304 and 306 are suitably connected to the body of assembly 206 with fasteners such as screws or bolts, although any other suitable attachment means may also be used.

FIGS. 3C and 3D illustrate section views taken along section lines 3C-3C and 3D-3D of FIG. 3A. Sieve bed portion 300 includes first and second perforated inserts 316 and 318. A spring 320 is also provided and presses against insert 316, which in turn presses against the separation medium disposed between inserts 316 and 318. This insures that the physical separation medium is compressed between the inserts 316 and 318.

The space between perforated inserts 316 and 318 is filled with a physical separation medium or material. The separation material selectively adsorbs one or more adsorbable components of a gaseous mixtures such as, for example, a gaseous mixture of nitrogen and oxygen, and allows one or more nonadsorbable components of the gaseous mixture to pass. The physical separation material is a molecular sieve with pores of uniform size and essentially the same molecular dimensions. These pores selectively adsorb molecules in accordance with molecular shape, polarity, degree of saturation, and the like. In one embodiment, the physical separation medium is an aluminosilicate composition with 4 to 5 angstrom pores. In this embodiment, the molecular sieve is a sodium or calcium form of aluminosilicate, such as type 5A zeolite. Alternately, the aluminosilicate may have a higher silicon to aluminum ratio, larger pores, and an affinity for polar molecules, e.g. type 13× zeolite. In another embodiment, a lithium-based zeolite may be used. In other embodiments, any suitable zeolite or other adsorbent material may be used. The zeolites adsorb nitrogen, carbon monoxide, carbon dioxide, water vapor, and other significant components of air. Gases such as oxygen that have not been adsorbed in sieve bed portion 300 may be collected and stored in product tank portion 302.

FIG. 3E is a section view taken along line 3E-3E of FIG. 3D. Product tank portion 302 and insert 316 of sieve bed portion 300 are illustrated. FIG. 3F is a further section view along line 3F-3F of FIG. 3D and is shown in perspective. As illustrated in this embodiment, sieve bed portion 300 and product tank portion 302 are formed from a single extruded piece of material such as, for example, aluminum. Other materials capable of being extruded may also be used.

Sieve bed portion 300 and product tank portion 302 share a common wall portion and form an integrated sieve bed and product tank assembly. In particular, the inner spaces of sieve bed portion 300 and product tank portion 302 are at least partially bounded by a common wall structure. In this embodiment, the common wall structure is shown as a portion of an arcuate or curved wall that is shared by sieve bed portion 300 and product tank portion 302. In other embodiments, the common wall structure need not be arcuate or curved and can be linear or any other shape. Furthermore, other structures capable of being extruded may join otherwise separate sieve bed portions and product tank portions including, for example, web(s), projections, or extensions.

Still further, more than one sieve bed portion 300 and one product tank portion 302 many be formed by extrusion and connected as described herein. For example, sieve bed portion 300 shown in FIG. 3F may share a common wall structure with multiple product tank portions 302, which may partially or fully circumscribe sieve bed portion 300 in the same manner as product tank portion 302. Similarly, product tank portion 302 may share a common wall structure with multiple sieve bed portions 300.

Referring to now to FIG. 3G, an exploded perspective view of sieve bed and product tank assembly 206 is shown. As described earlier, assembly 206 includes end caps 304 and 306, which attach to sieve bed portion 300 and product tank portion 302. The attachment of end caps 304 and 306 is facilitated through seal members 322 and 324. As shown in FIG. 3G, seal members 322 and 324 have a physical geometry that matches the cross-section of the distal ends of sieve bed portion 300 and product tank portion 302. Seal members 322 and 324 are configured to receive the ends of sieve bed portion 300 and product tank portion 302. Seal members 322 and 324 are also configured to be received within a mating portion of end caps 304 and 305. In this manner, seal portions 322 and 324 provide a gasketing effect facilitating attachment of end caps 304 and 306 and sealing of the inner spaces of sieve bed portion 302 and product tank portion 304. Each seal portion includes components for sealing the sieve bed portion 300 and product tank portion 302. In other embodiments, seal members 322 and 324 may be omitted by providing a sealing portion within end caps 304 and 306.

FIG. 3H is a detail view of the upper portion of sieve bed and product tank assembly 206. Seal member 322 includes a plurality of recesses 326, 328, and 330, for example, for receiving the ends of sieve bed portion 300 and product tank portion 302. Each recess is walled and includes top portions 332, 334, and 336, for example. Top portions 332, 334, and 336 of seal member 322 are received within recesses 338, 340, and 342, for example, of end cap 304. End cap 304 recesses 338, 340, and 342, for example, are formed by walls that project from end cap 304. When end cap 304 is secured to sieve bed portion 300 and product tank portion 302 via fasteners, end cap 304 and sieve bed portion 300 and product tank portion 302 compress seal member 322 thereby providing a gas-tight seal. End cap 306 and seal member 324 are similarly configured. As described above, seal members 322 and 324 can be omitted and recesses 338, 340 and 342 in end cap 304 can be made to form a gas-tight seal.

Referring to now to FIGS. 3I-3L, and more particularly to FIG. 3J, perspective views of an alternate end cap design 350 is shown. End cap 350 differs from the previously described end cap 304 in that it includes an integrated sound attenuator or muffler. Whereas the embodiment of FIG. 2 includes discreet sound attenuators or mufflers 216 and 218, the embodiment of end cap 350 integrates a sound attenuator or muffler into its structure.

As shown in FIG. 3J, end cap 350 includes a body having a sieve bed/product tank interface portion 352. Interface portion 352 also serves as a base from which muffler portion 354 extends. Also extending from interface portion 352 is a mounting boss 356. A muffler block 358 is housed within muffler portion 354 and a perforated exhaust cap 360 closes muffler portion 354. Mounting boss 356 accepts a fastener that passes through exhaust cap 360 and muffler block 358. Alternative means for securing these components can also be utilized.

End cap 350 further includes an input port 362 and a fitting 364 that may be attached to it. In other embodiments, other types of fittings may be used. End cap 350 also includes an input port 365 to the muffler portion 354. Input port 365 is connected to muffler portion 354 through passageway 367. In this manner, gases exhausted from the sieve bed are input through port 365 and passageway 367 into muffler portion 354. The gases are then exhausted by muffler portion 354 through perforated end cap 360.

Referring now to FIGS. 3M and 3N, and particularly to FIG. 3N, an exploded sectional view of end cap 350 is shown. Sieve bed/product tank interface portion 352 is shown having walled structures similar to end cap 304 for accepting a seal member similar to seal member 322 (See FIG. 3F and its accompanying text). Muffler portion 354 has walls that extend from interface portion 354 so as to form a perimeter bounding space 366. Mounting boss 356 also extends from interface portion 352 and resides in space 366.

Muffler block 358 is porous and includes a bore or hole 368 extending therethrough. The bore or hole 368 is sized so that mounting boss 356 can be received therein to hold and retain muffler block 358. In other embodiments, muffler block 358 can be semi-porous having non-porous portions or can be made of any other sound-deadening material. Muffler block 358 is disposed proximate interface portion 352 within space 366, though it can sized so as to at least partly fill space 366. As gases are exhausted, muffler block 358 may be displaced so as to reside more proximate or against perforated cap 360 (see FIG. 3O showing un-displaced position).

Perforated cap 360 includes a plurality of holes for exhausting gases introduced into muffler portion 354. Cap 360 includes a base portion having the holes and walls that extend therefrom so as to form a space 370. End cap 360 and its walls are structured to receive an end section of muffler portion 354 therein. This is accomplished by providing the walls of cap 360 with a shoulder portion for abutting against the end section of the muffler portion 354. A fastener then passes through cap 360 and interfaces with boss 356 to hold the two components together. Other means of fastening can also be used including snap clips, glue, ultrasonic welding, etc. FIG. 3O shows a cross-sectional perspective of end cap 350 illustrating the assembled structure.

Vacuum Pump Assembly

Referring now to FIG. 4A, a perspective view of vacuum pump assembly 210 and rear housing portion 106 is shown. Vacuum pump assembly 210 has frame 406 within which compressor 408 is mounted or suspended. Rear housing portion 106 has slots 400 and 402 that interface with the vacuum pump assembly 210. Frame 406 has tabs such as, for example, tab 404, which are received in slots 400 and 402 to locate and secure the vacuum pump assembly 210 to the rear housing portion 106. Other means of mounting vacuum pump assembly 210 to rear housing portion 106 can also be employed such as, for example, brackets and fasteners.

FIG. 4B is an exploded perspective view of the vacuum pump assembly 210. Vacuum pump assembly 210 includes vacuum pump 408, a multi-piece interface bracket having members 420, 422, and 424, frame 406, and a plurality of suspension members 430. Interface bracket member 420 includes a plurality of hook-type portions 428 that couple with apertures 426 in interface bracket members 422 and 424. FIG. 4C illustrates the interface bracket when members 420, 422 and 424 are coupled together. The interface bracket is coupled or affixed to a body of vacuum pump 408 through appropriate fastening means such as, for example, screws, bolts, clips, or pins.

Still referring to FIG. 4B, suspension members 430 include enlarged end portions that are connected together through elongated central portions. Suspension members 430 are resilient in that they can be stretched under tension. In one embodiment, suspension members 430 are formed from an elastomeric material such as, for example, rubber. In other embodiments, suspension members 430 can be made of metal to form resilient springs.

Frame 406 includes a plurality of structural support members generally forming a cage-like structure having a top 414, bottom 416, and sides 412 and 418. The corner portions of frame 406 include openings or apertures 434 that are used in conjunction with suspension members 430 to mount or suspend vacuum pump 408 within frame 406 as shown in FIG. 4A.

Referring now to FIG. 4D, a sectional view of vacuum pump assembly 210 with vacuum pump 408 removed is shown. Interface bracket member 424 is shown and includes hook portions 432 that interface with suspension members 430. In particular, the enlarged end portions of suspension members 430 are inserted within the eye of hook portions 432 and the recesses or openings 434 of frame 406. While FIG. 4D illustrates the suspension or mounting of interface bracket 424 within frame 406, interface bracket 422 is similarly suspended or mounted within the frame 406 thereby suspending or mounting vacuum pump 408 within frame 406.

Configured as such, vacuum pump 408 is suspended or mounted relative to frame 406 in a manner that isolates the movement or vibration of vacuum pump 408. The movement or vibration of vacuum pump 408 is isolated through elastic suspension members 430. Elastic suspension members 430 allow vacuum pump 408 to move within frame 406 without translating that movement to frame 406. In this embodiment, a total of eight suspension members 430 are employed at the corners of frame 406 but this need not to be the case. Any number of suspension members may be used at any location(s) with respect to frame 406 and vacuum pump 408 in a manner that suitably allows vacuum pump 408 to move relative to frame 406 without translating that movement to frame 406.

Referring now to FIG. 4E, a second embodiment of a suspension member is shown in the form of suspension member 436. Suspension member 436 is similar to suspension members 430 in that it structurally incorporates a plurality of suspension members 430. As shown, suspension member 436 incorporates four individual suspension members 430. Suspension member 436 further includes connective portions 438 that connects together the individual suspension member portions 430 to form a unitary whole. In other embodiments, suspension member 436 need not be formed as a continuous structure but may also form an open structure such as, for example, by omitting one of the connective portions 438 shown in FIG. 4E. Another configuration that provides for the physical communication of individual suspension members 430 can also be employed.

Suspension member 436 is connected to interface bracket members 422 and 424 in the same manner as described for the individual suspension members of 430. That is, the enlarged end portions 440 of suspension members 430 are inserted into the eye of hook portions 432 of the interface bracket members and the enlarged end portions 442 are inserted into the openings or recesses 434 of frame 406. It may be that in some cases suspension member 436 allows for easier assembly of vacuum pump assembly 210. In the embodiment shown, two suspension members of 436 would be required to replace the eight suspension members 430 shown in FIG. 4B. FIG. 4F illustrates yet another embodiment of vacuum pump assembly 210 having and interface bracket with circular end portions that are suspended within a frame by suspension members 430.

Configured as such, vacuum pump assembly 210 reduces noise, vibration, and vibration induced noise that may emanate from the vacuum pump during operation. Also, vacuum pump assembly is configured that vacuum pump 408 may be mounted within frame 408 according to a plurality of orientations. The interface bracket members 420, 422 and 424 and frame 406 can be made of any suitable material including, for example, metal or plastic or combinations thereof. In addition, the vacuum pump 210 has a pump inlet and a pump outlet for allowing gas flow through the vacuum pump 210.

Scavenger Pump Assembly

A pump assembly 211 may also be included in the oxygen concentrator 100 to increase the pressure of the concentrated oxygen provided to the user. In various embodiments, the concentrated oxygen may be produced and/or stored at pressures around atmospheric pressure (i.e., ambient room pressure) or below atmospheric pressure (sub-atmospheric pressure). In these embodiments, it may be desirable or necessary to increase the pressure of the concentrated oxygen for delivery to the user. This pump 211 may be referred to, for example, as a scavenger pump, an accumulator pump, a booster pump, etc. Exemplary pumps include, for example, WOB-L Piston Air Compressors and Vacuum Pumps, including models 8003, 8005, 8006, and 8009. These include single head, dual head, and speed adjustable pumps with various specifications. The mounting and isolation of the scavenger pump 211 may be similar to the structure described above for the vacuum pump assembly 210. In some embodiments, the scavenger pump 211 may be isolation mounted to a base with rubber grommets or the like. In this manner, the scavenger pump assembly reduces noise, vibration, and vibration induced noise that may emanate from the scavenger pump 211 during operation. In addition, the scavenger pump 211 has a pump inlet and a pump outlet for allowing gas flow through the scavenger pump 211.

In other embodiments, as shown in FIGS. 2B and 2C, instead of including a separate scavenger pump 211, a combination vacuum/scavenger pump assembly 210′ may be utilized to perform the functions of the vacuum pump assembly 210 and the scavenger pump 211. In these embodiments, the vacuum/scavenger pump assembly 210′ may have more than one pump inlets and pump outlets for allowing gas flow through the vacuum/scavenger pump assembly 210′ in more than one flow path.

The exemplary vacuum pump 210, combination vacuum/scavenger pump assembly 210′, and/or scavenger pump 211 may include any known gas pumping technology, such as, for example, rotary compressors/pumps, linear compressors/pumps, pressure intensifiers, etc.

Accumulator

An accumulator 209 may also be included in the oxygen concentrator 100. As discussed in more detail below, the accumulator 209 may be used to store concentrated oxygen pressurized by the scavenger pump 211, including at a pressure above ambient pressure. The mounting and structure of the accumulator 209, including similar input and outlet ports, may be similar to that of the product tank 302 of the exemplary sieve bed and product tank assemblies 206, 208. In other embodiments, the accumulator 209 can be any device capable of storing a quantity of gas, such as, for example, a tank, vessel, or coil tubing.

In other embodiments, as shown in FIGS. 2A and 2C, instead of including a separate accumulator 209, a sieve bed and accumulator assembly 208′ may be utilized. In these embodiments, the sieve bed and accumulator assembly 208′ performs the functions of the accumulator 209 and the sieve bed 300 of the sieve bed and product tank assembly 208, while the product tank 302 of the other sieve bed and product tank assembly 206 performs all of the product tank 302 functions.

FIG. 4G is a block diagram 450 showing the gas pressure stages of an exemplary concentrator, such as concentrator 100. In this embodiment, using the exemplary assembly described above, the concentrator 100 draws air, including oxygen, nitrogen, and other gases, at ambient or atmospheric pressure, into the concentrator 100. The air may be drawn into the concentrator 100 because of a pressure difference between the ambient air (P_(atm)) and a sub-atmospheric pressure (−P1) created within the concentrator by a vacuum pump as part of vacuum swing adsorption process, described in more detail below. At 452, oxygen may be separated from the air at a sub-atmospheric pressure −P1 using a sieve bed, such as sieve beds 300. At 454, the concentrated oxygen may be provided or stored at a sub-atmospheric pressure −P2, such as in product tanks 302. Concentrated oxygen may also be provided or stored at or near atmospheric pressure P, as shown at block 458. In some embodiments, during the vacuum swing adsorption process, the pressure at a particular stage may change as the active sieve bed fills or as the process equalizes near ambient pressure.

Although a user may draw gas from the concentrator 100 during inhalation, providing the concentrated oxygen at a pressure above atmospheric pressure (+P) may assist delivery of the concentrated oxygen to the user. In these embodiments, the source of the oxygen is provided at a positive pressure (+P), which is greater than atmospheric pressure (P_(atm)). The oxygen provided or stored at sub-atmospheric pressures (−P1, −P2), as shown by 456, and in some cases the near atmospheric pressure (P), as shown in 458, will require a pressure boost to a positive pressure (+P), as shown in 460. Concentrated oxygen boosted to the positive pressure +P can then be delivered to the user of the concentrator 100, such as a patient. The pressure boost may be provided by the scavenger pump 211.

Variable Bleed Valve

Another embodiment of a concentrator includes an optional variable bleed valve 502. In some embodiments, the bleed valve 502 is not included or utilized because the regeneration of the nitrogen rich bed 300 is accomplished by use of the flow created by the vacuum pump 408. Referring now to FIGS. 5A and 5B, concentrator 500 includes optional bleed valve 502 and an optional fixed orifice 514 in series and in pneumatic communication with sieve beds 300. In operation, a flow setting input 504 is selected by a user and received by a microprocessor-based controller 506. Controller 506 has associated therewith memory and logic for controlling the operation of, for example, the vacuum pump 408, main valves MV1 and MV2, entrance valves EV1 and EV2, conserver valve 512, pressure equalization valve PE, and bleed valve 502. All of these valves may be solenoid controlled. In one embodiment, the vacuum pump 408 is run at a variable speed based on the flow setting input 504. For example, low flow settings allow for the vacuum pump 408 to be run at a slower speed thereby conserving energy. The vacuum pump 408 can be run at higher speeds for higher flow settings. For example, the controller 506 may run the vacuum pump 408 at various settings, for example, certain revolutions per minute (rpm) with respect to the lowest to highest flow setting inputs 504. Of course, other speed values are envisioned and any suitable speed value may be implemented. Controller 506 also receives input from a vacuum/pressure sensor 510.

The flow setting input 504 is received by controller 506. The flow setting input 504 may designate a flow rate that the user desires for delivery of the product gas (e.g., oxygen) in a pulsed output mode. For example, a plurality of flow input settings 504 may include 300 cc/min (e.g., 15 cc/pulse at 20 breaths per minute (bpm)), 460 cc/min (e.g., 23 cc/pulse at 20 bpm), 620 cc/min (e.g., 31 cc/pulse at 20 bpm), 740 cc/min (e.g., 37 cc/pulse at 20 bpm), or 840 cc/min (e.g., 42 cc/pulse at 20 bpm). Based on this setting, controller 506 appropriately controls the vacuum pump 408 and valves to deliver the desired pulsed output flow of oxygen. Of course, other flow rate values are envisioned and any suitable flow rate value may be implemented. Additionally, the flow setting input 504 may designate a flow rate that the user desires for delivery of the product gas in a continuous output mode.

Generally, the concentrator operates using a vacuum swing adsorption (VSA) process. The vacuum pump 408 draws gas, through main valves MV1 and MV2, in an alternate fashion from sieve beds 300. In this manner, the vacuum pump 408 purges sieve beds 300 and creates a pressure in the sieve tanks that is less than ambient pressure. After drawing a vacuum or sub-ambient pressure into a sieve bed 300 through main valve MV1 or MV2, an entrance valve EV1 or EV2 is opened to allow room air, at ambient pressure, to flow into the sieve bed 300, creating concentrated oxygen at the sieve bed 300 output. Oxygen exiting the sieve bed 300 is available for use by the patient via the patient port or can be stored in the product tank(s) 302 (and/or accumulator 532, as described below). While one sieve bed 300 is being filled, the other sieve bed 300 is typically being purged of its contents. Each sieve bed 300 is filled with a nitrogen adsorbing material so that nitrogen gas is trapped within the sieve bed 300 and oxygen gas is allowed to pass to the product tank 302. When a particular sieve bed 300 has reached its adsorption capacity, which can be known by its output pressure or the oxygen purity of its gas output, the adsorbed gases, such as nitrogen, must be purged before the sieve bed 300 can be used again.

In a VSA system, the pressure of the product gas at the product tanks 302 may vary throughout the VSA process and may be different in various embodiments. For example, the pressure of the product gas at the product tanks 302 may be at a near ambient pressure (e.g., P, as shown in FIG. 4G) and/or may be at a sub-ambient pressure (e.g., −P1 and/or −P2, as shown in FIG. 4G). The scavenger pump 530 may be used to provide pressurized oxygen or an increased flow of oxygen to the patient via the patient port at some pressure above ambient room pressure (e.g., +P, as shown in FIG. 4G). The scavenger pump 530 may draw oxygen from the product tanks 302 and/or directly from the filling sieve bed 300. In this manner, the scavenger pump 530 may also reduce the pressure at the product tanks 302. The scavenger pump 530 may be used to help initialize and/or maintain the sub-ambient pressure at the oxygen side of the sieve bed 300, which may be used to improve the productivity of the adsorption cycle/oxygen production cycle.

An accumulator 532 may also be used to store excess oxygen not required by the patient, for example, based on the current flow setting 504 or in conjunction with the timing of the conserver valve 512, described in detail below. Oxygen from the accumulator 532 may be utilized in several situations, such as, for example, during VSA switch-over periods (i.e., utilized similar to the product tanks 302), during periods when the scavenger pump is OFF, or during periods when the VSA system is OFF. Utilization of the scavenger pump 530 and accumulator 532 may be based on factors associated with minimizing total energy usage of the system 500. As mentioned above, the accumulator 532 can be any device capable of storing a quantity of gas, such as, for example, a tank, vessel, or coil tubing.

In other embodiments, a pressure switch and/or sensor 534 may be used to start and stop the scavenger pump 530. For example, as the scavenger pump 530 builds positive pressure oxygen in the accumulator 532, once a predetermined pressure is reached in the accumulator 532, a signal from the pressure switch/sensor 534 could be used to turn off the scavenger pump 530. The pressure switch/sensor 534 could be used to turn on the scavenger pump 530 when another predetermined pressure is reached in the accumulator 532. The value associated with the predetermined pressures to turn the scavenger pump 530 on and off may be different, providing hysteresis. In some embodiments, the pressure switch/sensor 534 may be a pressure switch to control the actuation of the scavenger pump 530. In other embodiments, the pressure switch/sensor 534 may be a pressure sensor that can send an output signal to the controller 506, which can control the actuation of the scavenger pump 530 based on the sensed pressure. Turning the scavenger pump 530 on and off may be desirable, for example, to reduce energy usage of the scavenger pump 530 or maintain a safe pressure at the accumulator 532. The pressure of the oxygen in the accumulator 532 may increase in various situations, such as, for example, if oxygen usage is below the expected usage (e.g., if for some reason the patient didn't request a breath for a long period of time) or if the usage flow rate is lower than the fill rate of the accumulator 532.

Pressure equalization valve PE allows for a more efficient generation of oxygen by equalizing the pressure between the output lines of a sieve tank nearing fill completion and a sieve tank nearing the end of its purge cycle. U.S. Pat. Nos. 4,449,990 and 5,906,672, which are incorporated herein by reference, further describe the operation of pressure equalization valves. The oxygen that is being output by a particular sieve bed 300 may be stored in one or both product tanks 302. Both product tanks 302 are utilized in the embodiment of FIG. 5A.

As mentioned above, controller 506 can detect when the sieve bed 300 being filled has reached its adsorption capacity via vacuum/pressure sensor 510. As shown in FIG. 5B, in one embodiment, vacuum/pressure sensor 510 provides a signal indicative of pressure at the product tank side of a first check valve 516 that passes oxygen flow from the filling sieve bed 300 to interconnected product tanks 302 and a second check valve 516 that blocks oxygen flow from the interconnected product tanks 302 to the other sieve bed 300 while it is being regenerated. For example, the signal may reflect the difference between the oxygen gas and ambient air. In other embodiments, the vacuum/pressure sensor 510 may be located anywhere in fluidic communication with the output of the sieve bed 300 being filled. Multiple vacuum/pressure sensors 510 may be implemented if directly monitoring the output of each sieve bed 300 is desired. An additional pressure sensor, such as pressure switch/sensor 534 may also be used in other embodiments to monitor the positive pressure of the oxygen delivered to the patient, for example, on the output side of the scavenger pump, as described in more detail below. Once the filling sieve bed 300 has reached its capacity, controller 506 shifts the filling sieve bed 300 into a purging or exhausting cycle and shifts the other sieve bed 300, which is now regenerated, to a filling cycle. This is the basic repetitive, alternating operation of the VSA process. For example, the controller 506 may shift or alternate cycles for sieve beds 300 when the vacuum/pressure sensor 510 detects various pressure and/or vacuum levels, for example, different pounds per square inch gauge (psig) readings, with respect to the lowest to highest flow setting inputs 504. Of course, any particular and suitable psig value may be implemented.

In one embodiment, bleed valve 502 has a variable “on delay” before activation to an open or “on” state. The variable “on delay” is associated, in one embodiment, with the flow setting input 504. For example, the controller 506 may activate the bleed valve 502 after an “on delay” of 3.3 seconds (sec), 3.2 sec, 3.0 sec, 2.9 sec, and 2.8 sec, with respect to the lowest to highest flow setting inputs 504. Of course, other “on delay” values are envisioned and any suitable “on delay” value may be implemented. In one embodiment, bleed valve 502 is de-activated by the controller 506 after the filling sieve bed 300 has reached its capacity in conjunction with the end of the corresponding filling cycle (i.e., the start of the next filling cycle for the other sieve bed 300). In general, bleed valve 502 can selectively “bleed” oxygen out of one sieve bed 300 and into the other sieve bed 300 at a flow rate that is restricted by orifice 514. That is, oxygen is allowed to flow from the sieve bed 300 being filled to the sieve bed 300 being exhausted or purged. This oxygen flow can assist the exhausting or purging of the sieve bed 300 to expel its captured nitrogen and to regenerate itself for its next filling cycle. Since the vacuum pump 408 is variably filling a sieve bed 300 based on the flow setting input 504, a bleed flow between the sieve beds 300 that can be variably controlled can assist in the efficient purging of the exhausting sieve bed 300 for the corresponding product gas output flow rate of the concentrator at a suitable purity level.

Generally, the higher the value of the flow setting input 504, the shorter the “on delay” time (i.e., closed time) and the longer the time that the bleed valve 502 will be open with more bleed flow being sent to the exhausting sieve bed 300. This is because higher pressurization levels may be used for the higher values for flow setting inputs 504. The higher pressurization levels may require more bleed flow to regenerate the exhausting or purging sieve bed 300. Conversely, the lower the value of the flow setting input 504, the longer the “on delay” time (i.e., closed time) and the shorter the time that the bleed valve 502 will be open. This is because lower pressurization levels may be used for the lower values for flow setting inputs 504. The lower pressurization levels may require less bleed flow to regenerate the exhausting or purging sieve bed 300. Accordingly, the variable “on delay” logic described above allows for an increased level of system efficiency in terms of maximizing the utilization of the oxygen that is generated by controlling the amount used in the purging of an exhausting sieve bed 300. In other embodiments, other variable logic may be used to vary other control parameters (e.g., bleed flow duration) for the bleed valve 502 for different flow setting inputs 504. In further embodiments, the variable logic may use other sensed parameters (e.g., pressure) to vary the “on delay” or other control parameters for different flow setting inputs 504.

As described above, the “on delay” time period prior to activation of the bleed valve 502 is dependant upon the value for the flow setting input 504 which in turn is based on certain other operating parameters, such as product tank output pressure, sieve tank output pressure, vacuum pump speed, and volumetric capacity of various components. In one embodiment, the specific “on delay” time period for each flow setting input 504 may be determined empirically based on the physical specifications of the concentrator components. The “on delay” times for each value for the flow setting input 504 are then stored in a look-up table in the memory or logic of controller 506. Hence, after reading the flow setting input 504, controller 506 looks up the bleed valve variable “on delay” time from the look-up table stored in its memory or logic. The corresponding “on delay” time is then used to delay activation of the bleed valve 502 from the start of the filling cycle for the sieve bed 300 providing the bleed flow. As shown, the filling cycle starts after the pressure equalization valve PE closes (see timing diagram of FIG. 5D). Upon expiration of the “on delay” time, which can be monitored by a timer in the memory or logic, the bleed valve 502 may be activated (i.e., opened or “on”) and can remain open until the start of the next VSA cycle in which the roles for the two sieve beds 300 is shifted.

In other embodiments, the variable “on delay” may be based at least in part on a minimum “on delay” time. In another embodiment, the variable “on delay” may be based at least in part on one or more other parameters, such as product tank output pressure, sieve bed output pressure, vacuum pump speed, and volumetric capacity of various components in any combination. In still other embodiments, the variable “on delay” may be based at least in part on a minimum “on delay” time in combination with one or more other parameters. For example, after the minimum “on delay” time, activation of the bleed valve 502 may be triggered if the other parameter exceeds a predetermined threshold at that time or any time before the current filling cycle is complete. Of course, alternate or opposite logic is envisioned and any suitable logical relation between the parameter and threshold may be implemented. In still other embodiments, activation of the bleed valve 502 may be triggered if the other parameter exceeds the predetermined threshold at any time during the filling cycle without a minimum “on delay.”

In any of the embodiments described herein, bleed valve 502 may also have a variable “maximum on time” after activation in order to limit the continuous time it remains open or in the “on” state. The variable “maximum on time” may be associated with the flow setting input 504. For example, the controller 506 may de-activate the bleed valve 502 after a “maximum on time” of 2.2 sec, 2.4 sec, 2.6 sec, 2.8 sec, and 3.0 sec, with respect to the lowest to highest flow setting inputs 504. Of course, other “maximum on time” values are envisioned and any suitable “maximum on time” value may be implemented. In this embodiment, the bleed valve 502 would also be de-activated if the end of the current filling is reached before the “maximum on time” expires. Conversely, if the “maximum on time” expires before the end of the current filling cycle is reached, the bleed valve 502 could be activated again based on any combination of the “on delay” time or parameter triggers described above. If desired, the bleed valve 502 may also be fixed to provide a continuous bleed or fixed to a predetermined open time that is independent of the flow setting input 504. Additionally, the “on delay” time may be set to zero for a particular flow setting input 504 to provide a continuous bleed and the “maximum on time” may be set to zero for a particular flow setting input 504 to inhibit activation of the bleed valve 502.

FIG. 5C illustrates another embodiment of a concentrator 550 that includes a high pressure product tank 552 and a low pressure product tank 554. Comparing the concentrator 550 of FIG. 5C to the concentrator 500 of FIG. 5A, the low pressure product tank 554 (FIG. 5C) replaces the product tanks 302 (FIG. 5A) and high pressure product tank 552 (FIG. 5C) replaces the accumulator 532 (FIG. 5A). The low pressure product tank 554 can store oxygen from the filling sieve bed 300 at around an ambient room pressure. The high pressure product tank 552 can store oxygen from the scavenger pump 530 at a pressure above ambient room pressure. In this embodiment, two sieve bed and product tank assemblies 206 may be utilized for a system including an above-ambient storage vessel (e.g., high pressure product tank 552) without the addition of an accumulator 532.

FIG. 5D illustrates one embodiment of a timing diagram for the valves shown in FIG. 5A. As shown, after the first filling cycle, each filling cycle begins when the pressure equalization valve PE transitions from closed (i.e., off, de-activated) to open (i.e., on, activated). For example, upon the first activation of pressure equalization valve PE, oxygen from the second sieve bed 300 (i.e., associated with main valve MV2) flows through the pressure equalization valve PE to increase the pressure in the first sieve bed 300 (i.e., associated with main valve MV1). Prior to the first activation of pressure equalization valve PE, main valve MV1 had been on, allowing the vacuum pump 408 to draw down the pressure of the first sieve bed 300 to below ambient room pressure, and entrance valve EV2 had been on, allowing ambient pressure room air to flow into the second sieve bed 300. Therefore, the first activation of pressure equalization valve PE allows oxygen from the second sieve bed 300 to flow through the pressure equalization valve PE to increase the pressure in the first sieve bed 300. In addition to pressure equalization, this oxygen transfer from one sieve bed 300 to the other, through the pressure equalization valve PE, preloads the top of the receiving sieve bed 300 with oxygen for use as that sieve bed 300 starts its filling cycle. Entrance valve EV2 is de-activated along with this activation of pressure equalization valve PE or shortly thereafter if the pressure equalization valve PE is to be used to assist in purging and regeneration of the first sieve bed 300. Shortly after this activation of the pressure equalization valve PE, main valve MV1 is de-activated and main valve MV2 is activated to switch exhaust gas flow generated by the vacuum pump 408 from the first sieve bed 300 to the second sieve bed 300. The pressure equalization valve PE is de-activated shortly after the main valves MV1 and MV2 are switched. Typically, entrance valve EV1 is activated along with this de-activation of pressure equalization valve PE to permit pressure equalization between the sieve beds 300 to continue. However, if desired, the entrance valve EV1 could be activated along with de-activation of main valve MV1 or shortly thereafter and before de-activation of pressure equalization valve PE.

This process continues in alternating fashion to provide the VSA process. In other embodiments, main valves MV1 and MV2 may be switched in a “make before break” sequence, where the opening main valve opens shortly before the closing main valve closes. In this manner, one of the main valves MV1 and MV2 is always open. The delay between the opening and the closing of the main valves MV1 and MV2 may be relatively short. This type of switching, although not shown, may be utilized wherever the main valves MV1 and MV2 are shown switching in FIG. 5D.

In particular, it can be seen that the bleed valve 502, when used, may be generally closed or “off” while the pressure equalization valve PE is open or “on,” though this need not necessarily be the case. It can also be seen that the variable “on delay” time for the bleed valve begins when the pressure equalization valve PE transitions from closed or “off” to open or “on,” though this need not be the case as well. It may be beneficial under some circumstances to allow overlapping of the open or “on” states of these valves. In other words, under certain circumstances, both the bleed valve 502 and the pressure equalization valve PE may be utilized simultaneously or in any combination to provide bleed flow from the filling sieve bed 300 to the other sieve bed 300 for its purging and regeneration.

FIG. 5E shows an exemplary path for flow from sieve bed 1 through orifice 1 and sieve bed 2 to an exhaust gas outlet when entrance valve EV1, bleed valve 502, and main valve MV2 are activated (i.e., open) and entrance valve EV2 and main valve MV1 are de-activated (i.e., closed). FIG. 5F shows an exemplary alternate path for flow from sieve bed 2 through orifice 1 and sieve bed 1 to the exhaust gas outlet when entrance valve EV2, bleed valve 502, and main valve MV1 are activated and entrance valve EV1 and main valve MV2 are de-activated. As shown by dotted lines, in one embodiment, the functions of bleed valve 502 and orifice 1 may be provided in a single component which may be referred to as a variable restrictor. In another embodiment, orifice 2 may provide a continuous fixed flow in parallel to bleed valve 502 and orifice 1. Orifice 2 would establish a minimum flow which could be increased by activation of the bleed valve 502 as described herein. In still another embodiment, a pressure equalization valve PE may be selectively activated to provide or supplement flow in combination with orifice 2 or the series combination of bleed valve 502 and orifice 1.

In another embodiment, the controller 506 may monitor the VSA shifting time (i.e., filling cycle time) to identify alternate modes of operation for certain Earth altitude ranges in which the concentrator is being operated. For example, a low altitude mode may be implemented for operation up to approximately 6,300 feet and a high altitude mode may be implemented for operation above 6,300 feet. Of course, other altitude ranges are envisioned and additional altitude modes may be implemented. VSA shifting time tends to increase at higher altitudes due to lower ambient atmospheric (“room”) pressures (i.e., thinner air). Certain operating parameters of the concentrator may be adjusted based on a given altitude range in order to improve efficiency and sustain suitable levels of product gas volumetric output, flow rate, and purity.

A fixed “on delay” for bleed valve 502 based on flow setting input 504 may be acceptable in a low altitude mode of operation. However, the higher the altitude, the longer the shift time between filling of alternate sieve beds 300 because the concentrator takes longer to build up to the desired shift pressure. In response to the longer shift times, the concentrator may shift to a higher altitude mode which may adjust one or more operating parameters (i.e., product tank output pressure, accumulator pressure, sieve bed output pressure, bleed valve control) to keep the shift time in an optimum range. If a fixed “on delay” for the bleed valve 502 were maintained across a wide altitude range there may be little or no bleed flow at the lower elevations of the altitude range. Moreover, the fixed “on delay” could result in too much bleed flow at higher elevations when the shift time has been significantly stretched out. No bleed flow and too much bleed flow may result in the product gas from the concentrator being outside desired purity levels for operation at the lower and higher elevations of a wide altitude range.

It should be noted that use of the term “pressure” throughout this application includes pressures that are below atmospheric pressure, including, for example, negative pressures, less than ambient pressures, and sub-atmospheric pressures, as well as pressures at or above atmospheric or ambient pressure.

Suitable shift time thresholds may be established for transitioning from low altitude mode to high altitude mode (e.g., approximately 12 seconds) and for transitioning from high altitude mode to low altitude mode (e.g., approximately 5.5 seconds). Of course, different shift time thresholds can be established for different flow setting inputs 504. For example, the shift time thresholds for transitioning from low altitude mode to high altitude mode could range between 10.5 and 14 seconds for different flow setting inputs 504. Similarly, the shift time thresholds for transitioning from high altitude mode to low altitude mode could range between 5.0 and 5.5 seconds for different flow setting inputs 504. Typically, the thresholds will be different and the threshold for transitioning from high altitude mode to low altitude mode will be less than the other threshold to establish a suitable hysteresis. In another embodiment, transition between altitude modes can be delayed for a fixed time or until the shift times for a predetermined quantity of consecutive filling cycles (e.g., three consecutive cycles) indicate that the altitude mode transition is appropriate.

The bleed valve 502 may be controlled in any manner described herein for any altitude mode. Notably, the bleed valve 502 may be controlled differently in different altitude modes. Accordingly, preferred bleed valve control techniques can be implemented based at least in part on altitude mode and transitions in altitude modes can produce corresponding transitions in bleed valve control techniques.

In one embodiment, an “on delay” time associated with activation the bleed valve 502 and the VSA shifting time (i.e., filling cycle time) may have a generally linear relation encompassing the range of the flow setting inputs 506. The shift time may be represented by the shift pressure set-point for each flow setting input 506 because the shift time is the time it takes a given sieve bed 300 to reach a pressure related to its full capacity. In the embodiment being described, pressure build in the sieve bed 300 may be assumed to be linear. This allows a bleed valve activation pressure to be expressed as a ratio of pressure set-point for each flow setting input 506. The ratio may then be used to determine a threshold pressure value. During the pressure build up, if the pressure exceeds the threshold pressure value, the controller 506 activates (i.e., opens) the bleed valve 502. This may ensure there is at least enough bleed flow to maintain a desired level of purity while also limiting bleed flow to avoid unnecessary loss of oxygen. In other embodiments, the “on delay” time may be a non-linear function of the VSA shifting time. Similarly, the function used to determine the “on delay” time may be different for different flow setting inputs 506 in other embodiments.

In another embodiment, the controller 506 may utilize a timer function to monitor VSA cycle shift time. This monitored shift time measurement may be compared against shift time ranges stored in non-volatile memory. The controller 506 may use the result of this comparison to determine if the concentrator should be operating in low or high altitude modes. In low altitude mode, for each flow setting input 504, the concentrator may operate from a fixed pressure value that is stored in non-volatile memory. In high altitude mode, the concentrator may operate from a fixed pressure value for each flow setting input 504 that is based at least in part on the corresponding low altitude fixed pressure value.

In yet another embodiment, in low altitude mode, for each flow setting input 504, the concentrator may operate from a fixed “on delay” time for activation of the bleed valve 502 that is stored in non-volatile memory. In high altitude mode, the concentrator may operate from a variable bleed valve activation time that is scaled based on the fixed pressure value for each flow setting input 504 or the monitored VSA cycle shift time. The bleed valve scale factor may be calculated from the fixed pressure value or the monitored VSA cycle shift time.

The aforementioned functions can be performed either as software or controller logic. “Logic,” as used herein, includes but is not limited to hardware, firmware, software and/or combinations of each to perform a function(s) or an action(s), and/or to cause a function or action from another component. For example, based on a desired application or needs, logic may include a software controlled microprocessor, discrete logic such as an application specific integrated circuit (ASIC), or other programmed logic device. Logic may also be fully embodied as software.

“Software,” as used herein, includes but is not limited to one or more computer readable and/or executable instructions that cause a computer or other electronic device to perform functions, actions, and/or behave in a desire manner. The instructions may be embodied in various forms such as routines, algorithms, modules or programs including separate applications or code from dynamically linked libraries. Software may also be implemented in various forms such as a stand-alone program, a function call, a servlet, an applet, instructions stored in a memory, part of an operating system or another type of executable instructions. It will be appreciated by one of ordinary skill in the art that the form of software is dependent on, for example, requirements of a desired application, the environment it runs on, and/or the desires of a designer/programmer or the like.

The systems and methods of the present invention can be implemented on a variety of platforms including, for example, networked control systems and stand-alone control systems. Additionally, the logic, databases or tables shown and described herein preferably reside in or on a computer readable medium such as, for example, a Flash Memory, Read-Only Memory (ROM), Random-Access Memory (RAM), programmable read-only memory (PROM), electrically programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), magnetic disk or tape, and optically readable mediums including CD-ROM and DVD-ROM. Still further, the processes and logic described herein can be merged into one large process flow or divided into many sub-process flows. The order in which the process flows herein have been described is not critical and can be rearranged while still accomplishing the same results. Indeed, the process flows described herein may be rearranged, consolidated, and/or re-organized in their implementation as warranted or desired.

FIGS. 5G and 5H further illustrate an exemplary embodiment of a valve assembly 214 that can include bleed valve 502 and other components. In this embodiment, bleed valve 502, pressure equalization valve PE, a conserver valve 512, fixed orifice 514, fixed orifice 515, and check valves 516 of concentrator 500 are mounted or affixed to a block-like manifold body having a plurality of inlets, outlets and inner passageways connecting the inlets, outlets and valves as shown. So configured, the valve assembly 214 results in a space and weight savings that is adaptable to a portable oxygen concentrator and other devices. The configuration also allows for easy service and replacement of the valve assembly 214 should that be necessary. In other embodiments, the concentrator may include discrete components or any suitable combination of components in one or more valve assemblies. In particular, bleed valve 502 and fixed orifice 514 may be combined in a modular assembly. In another embodiment, the bleed valve 502, pressure equalization valve PE, a conserver valve 512, fixed orifice 514, fixed orifice 515, and check valve 516 of concentrator 550 are mounted or affixed to a block-like manifold body having a plurality of inlets, outlets and inner passageways connecting the inlets, outlets and valves as shown in FIGS. 5G and 5H, but connecting to high pressure product tank 552 and low pressure product tank 554 instead of product tanks 302.

Output Port

In one embodiment of the present invention, output port 108 includes a suitable air filter. Though the oxygen exiting the sieve and product tanks has already been filtered prior to the nitrogen-oxygen separation process, additional filtering may be of assistance to some patients. Referring now to FIG. 6A, the perspective view of one embodiment of output port 108 is shown. The output port 108 includes a main body 600, input 602, extension 604 and output 610. Input 602 is configured to meet with pneumatic tubing that delivers oxygen. The oxygen received through input 602 enters main body 600. Main body 600 includes a suitable filter therein such as, for example, a HEPA filter or other suitable filter, for the filtering the oxygen. Extension 604 includes a key surface 606 and threads 608. The surface 606 facilitates a proper orientation of the output port 108 during our assembly with the housing of the oxygen concentrator. Threads 608 facilitate fastening of the output port 108 to the housing of the oxygen concentrator via a HEX nut or other type of fastener. Output 610 is configured to mate with tubing that delivers the oxygen to the patient or a medical accessory.

Referring now to FIG. 6B, a day cross-sectional view taken along a section lines 6B-6B of FIG. 6A is shown. The filter of main body 600 is shown at 612. Filter 612 occupies a substantial portion of the inner space of main body 600 to filter the oxygen being received through input 602. As such, filter 612 has a shape and geometry that complements the shape and geometry of the inner space of main body 600. In one embodiment, filter 612 is made of a Boro-Silicate Glass microfiber and is hydrophobic. Filter 612 also provides for a filtration efficiency of greater than 99.99% for particle sizes 0.2 micrometers or greater. Other filters having less than all of these properties may be used as well.

In one embodiment, the main body 600 is made from a polypropylene material and its inner space provides for an effective filtration area of 3.5 cm². The main body material can be any suitable material and the filtration area can be made larger or smaller than described. In one embodiment, output port 108 is preferably fabricated by joining two sections that interface in the region of the main body 600 to form the entire output port 108. In this example, two sections are shown being divided by interface axis 614 extending through main body 600. Filter 612 is inserted into one of the sections forming part of the inner space of main body 600. The other section would then be joined through bonding or welding, thereby sealing filter 612 into the inner space of main body 600. In other embodiments, the two sections can be joined via mating threads or other non-permanent connections that would allow removal and replacement of filter 612.

Vacuum/Pressure Sensor Calibration and Conserver

FIG. 7 illustrates one embodiment of a process 700 for calibrating vacuum/pressure sensor 510 and/or pressure switch/sensor 534 within controller 506. The rectangular elements denote “processing blocks” and represent computer software instructions or groups of instructions. The diamond shaped elements denote “decision blocks” and represent computer software instructions or groups of instructions which affect the execution of the computer software instructions represented by the processing blocks. Alternatively, the processing and decision blocks represent steps performed by functionally equivalent circuits such as a digital signal processor circuit or an application-specific integrated circuit (ASIC). The flow diagram does not depict syntax of any particular programming language. Rather, the flow diagram illustrates the functional information one skilled in the art may use to fabricate circuits or to generate computer software to perform the processing of the system. It should be noted that many routine program elements, such as initialization of loops and variables and the use of temporary variables are not shown. Also the order flow may be changed with the same results being obtained.

The calibration routine, for example, may be performed by a qualified technician using an adjustable external pressure source. Of course, other scenarios are possible and any procedure that suitably accomplishes the sensor calibration may be implemented. In block 702, a signal (e.g., analog to digital count (A-D count)) from the sensor 510, 534 is read by the controller 506 after an external vacuum/pressure source is adjusted to a first fixed pressure setting (I) and pressure (or vacuum) is applied to the sensor 510, 534. For example, the first fixed pressure setting (I) may be a pressure associated with normal operation of the concentrator, such as 0 psig for sensor 510 or 10 psig for sensor 534. For example, controller 506 includes as one of its structures an analog-to-digital converter that allows it to read analog signals that emanate from sensors such as pressure and flow sensors. The conversion of an analog sensor signal to a digital or binary value allows the controller to read and use the sensor signal in its processing. In other embodiments, the first fixed pressure setting (I) can be any pressure setting including ambient or vacuum. In block 704, a value for the signal read in 702 (e.g., corresponding A-D count) is stored in memory.

In block 706, the signal (e.g., A-D count) from the sensor 510, 534 is read by the controller 506 after the external vacuum/pressure source is adjusted to a second fixed pressure setting (II). For example, the second fixed pressure setting (II) may also be a pressure associated with normal operation of the concentrator, such as −10 psig for sensor 510 or 20 psig for sensor 534. Similar to the first pressure setting (I), the second pressure setting (II) can be any pressure setting. Block 708 stores a value for the signal read in 706 (e.g., corresponding A-D count) in memory. Block 710 generates a linear extrapolation (Y=m(X)+B) using the first and second signal values (e.g., A-D count readings). The linear extrapolation is then used in block 712 by controller 506 to convert signal values (e.g., A-D counts) from the sensor 510, 534 to psig. In the linear extrapolation, X represents signal values (e.g., sensor A-D counts or readings) and Y represents pressure in psig. In alternate embodiments, any pressure setting can be used from unit-less or un-calibrated measures of pressure to external calibrated vacuum/pressure sources.

FIG. 8 illustrates one embodiment of a conserver process 800 for determining a time duration associated with providing a bolus of gas, such as oxygen, to a user of the oxygen concentrator 100. “Bolus,” as used herein includes, but is not limited to, a dose or pulse of concentrated product gas, such as oxygen, provided to the user via a suitable user interface, such as a nasal cannula or nasal mask. Bolus parameters relating to flow through pneumatic components include duration and amplitude. The duration parameter relates to activating and de-activating a valve to start and end the bolus. The amplitude parameter relates to flow capacity of the components and pressure of the product gas. Oxygen concentrator 100 can include, for example, a conserving device for controlling the flow of oxygen to the patient. For example, the conserving device may be adjustable in relation to one or more parameters to conserve power consumption of the oxygen concentrator 100 while maintaining suitable purity, flow rate, and volume of the product gas. In one embodiment, the conserving device is formed by controller 506, flow sensor 508, pressure sensor 534, conserver valve 512, and fixed orifice 515 (see, e.g., FIG. 5A). The conserver process 800 represents one embodiment of logic that can reside within controller 506. Also referring to FIG. 5B, controller 506 uses, for example, flow sensor 508 to monitor the breathing of a user to determine breathing characteristics (e.g., breath rate, inhalation, exhalation, volume, flow, etc.) of the user. Upon the start of inhalation (i.e., the end of exhalation), controller 506 is programmed to deliver a bolus of gas, such as oxygen, to the user. In this regard, the size of the bolus can be fixed or determined at least in part from the patient's breathing characteristics (e.g., breathing rate, duration of inhalation, volume, flow, etc.). Once fixed or determined, controller 506 controls the on and off state of conserver valve 512 to deliver the proper bolus of gas to the patient. For example, a bolus can be provided during the inhalation portion of each breathing cycle.

In block 802, the controller 506 has detected a trigger associated with the patient's breathing characteristics, determined that a bolus of gas is to be delivered to the patient, and opened or switched the conserver valve 512 to dispense concentrated product gas to the patient. A loop now begins where the controller 506 reads the signal (e.g., A-D count) of the pressure sensor 534 (block 802), converts the signal (e.g., A-D count) to psig (block 804), and sums the psig values until a pre-determined psig value is reached (block 806). For example, the pre-determined summation of psig values may relate to a pre-determined volumetric measure of concentrated breathing gas to be provided by the bolus. The pre-determined volumetric measure of concentrated breathing gas may be based at least in part on the patient's breath rate and a desired output volume over a pre-determined time duration (e.g., 300 cc/min). For example, the physical characteristics of the fixed orifice 515, the monitored pressure of the product tanks 302, and the time the conserver valve 512 is activated to provide product gas flow may be considered by the controller 506 in order to provide the desired volume of product gas in a given bolus. The relation of pressure over time for product gas flow through a fixed orifice is a classic integral calculus function. Where the pressure is variable, the time the conserver valve 512 is activated is adjustable in order to provide the desired volume of product gas. Accordingly, the controller 506 may control the conserver valve 512 based at least in part on the monitored pressure.

In block 804, the conversion from signal value (e.g., pressure sensor A-D count) to psig is accomplished using the linear extrapolation obtained from FIG. 7. In other embodiments, alternative methods of obtaining the psig values from the signal value (e.g., A-D counts) can also be utilized. In block 806, the psig values are summed by adding them together such as, for example, by the formula P=P+PSIG. In the formula, PSIG represents the current psig reading and P represents the current summation of pressures. This formula is derived from the classic integral calculus function defining the relation of pressure over time for product gas flow through a fixed orifice discussed above. In an alternative embodiment, the signal values (e.g., A-D counts) from the pressure sensor 534 can be summed until a pre-determined summation value (e.g., summation A-D count) is reached. Once the summation of pressures equals a pre-determined pressure summation threshold, at 810, the controller 506 closes the conserver valve 512 and waits for the next bolus trigger to occur. For example, the pre-determined pressure summation threshold may relate to a pre-determined volumetric measure of concentrated breathing gas to be provided by the bolus.

The pre-determined volumetric measure of concentrated breathing gas may be based at least in part on the patient's breath rate and a desired output volume over a pre-determined time duration (e.g., 840 cc/min). For example, the desired output flow rate setting (e.g., 840 cc/min) may be divided by the patient's breath rate to allocate the corresponding desired volume for the longer time scale to individual boluses for each patient breath. For an exemplary breath rate of 20 bpm, the desired volume for each bolus may be 42 cc. Similarly, for an exemplary breath rate of 10 bpm, the desired volume for each bolus may be 84 cc. Normally, a bolus would be delivered with each patient breath. However, the concentrator may intentionally skip a breath under certain circumstances to ensure that suitable product gas purity levels and system efficiency is achieved. For example, if the breath rate exceeds a predetermined rate (e.g., 36 bpm), the concentrator may not provide a bolus with every breath and may selectively skip breaths in a manner the achieves suitable product gas purity levels and system efficiency.

FIG. 9 illustrates one embodiment of timing operation of the conserver valve 512 with respect to a breathing characteristic (e.g., inhalation) associated with a user breathing cycle (i.e., BREATH 900). An exemplary breathing cycle 901 is shown with an inhalation period followed by an exhalation period. Flow sensor 508 measures a flow rate associated with the user breathing cycle when the conserver valve 512 is diverting user breathing through the vent port, which is represented by FLOW 902 and an exemplary flow signal 903 corresponding to the exemplary breathing cycle 901. Flow signal 903, for example, can represent analog signal levels, digital representations of analog signal levels, or actual flow rate units. In any event, trigger threshold 904 is established for flow signal 903. Trigger threshold 904 can, depending on the particular implementation, be a zero-crossing point, offset (positive or negative) from the zero-crossing point, an average flow per cycle, or off-set (positive or negative) from the average flow. In the embodiment shown in FIG. 9, the trigger threshold 904 is shown as occurring just after the inhalation phase has started. This is an example of a positive offset from the zero-crossing point. In one embodiment, the trigger threshold can be 12 standard cubic centimeters per minute (sccm).

Once the trigger threshold 904 has been reached by flow signal 903, controller 506 opens conserver valve 512 for a time duration long enough to deliver the required size bolus 905 to the user. In one embodiment, the time duration that the conserver valve 512 remains open may be determined by the logic of process 800 (FIG. 8). As described above in reference to FIG. 8, once the summation of pressures reaches the pre-determined summation value, conserver valve 512 is closed 906 by controller 506. The controller 506 may ignore or otherwise avoid taking action in relation to the trigger threshold 904 at least until a time duration associated with breath rates is exceeded in order to avoid triggering another bolus 905 before the start of the next inhalation. This may be referred to as a trigger lock-out period 907. The trigger lock-out period 907 can be determined as a percentage of a breathing characteristic (e.g., breath rate, breath cycle, exhalation, or other breathing characteristics including flow, flow rate and pressure) for an average person, exemplary person, or a particular person, such as the patient. For example, if a breath rate of 350 milliseconds (msec) is selected, the trigger lock-out period would be some percentage of 350 msec, such as 175 msec. This trigger lock-out period 907 ensures that the next trigger is not falsely or prematurely initiated until the start of the patient's next inhalation. After expiration of the trigger lock-out period 907, the next trigger threshold is active. In one embodiment, after the trigger lockout period, the controller 506 may also wait for the flow signal to fall below the trigger threshold 904 before enabling the next activation of the conserver valve 512. In this manner, a bolus 905 of gas (e.g., oxygen) may be delivered to the patient each time flow signal 903 rises through the trigger threshold 904 after the start of an inhalation portion of a breathing cycle. As described above, the concentrator may intentionally skip a breath under certain circumstances to ensure that suitable product gas purity levels and system efficiency is achieved.

The conserver valve 512 may also be controlled in any manner described herein for any altitude mode. Notably, the conserver valve 512 may be controlled differently in different altitude modes. Accordingly, preferred conserver valve control techniques can be implemented based at least in part on altitude mode and transitions in altitude modes can produce corresponding transitions in conserver valve control techniques.

In one embodiment, in high altitude mode, the controller 506 may automatically adjust operation of the conserver valve 512 to maintain suitable levels of purity, flow rate, and volume for the product gas as elevation changes. If not adjusted, for example, the conserver valve 512 may stay activated longer as the VSA cycle shift time increases in relation to higher elevations. This may result in larger bolus volumes than necessary and higher product gas outputs than desired. For example, in low altitude mode, the concentrator may operate using a low altitude fixed time duration for activation of the conserver valve 512 for a given flow setting input 504. The low altitude fixed time duration may be different for different flow setting inputs 504. Each low altitude fixed time duration may be a function of VSA cycle shift time and decay in pressure of the concentrated product gas associated with the shifting. These low altitude fixed time durations may be stored in non-volatile memory.

Similarly, in high altitude mode, the concentrator may operate using a high altitude fixed time duration for activation of the conserver valve 512 at a given flow setting input 504. The high altitude fixed time duration may be different for different flow setting inputs 504. Each high altitude fixed time duration may be a function of the low altitude fixed time duration for the corresponding flow setting input 504. The functional relationship between the low and high altitude fixed time durations may be different for different flow setting inputs 504. In other words, the algorithm defining the function at a given flow setting input 504 may be different from the algorithm defining the function at a different flow setting input 504. These high altitude fixed time durations may be stored in non-volatile memory. In other embodiments, values for certain parameters of the functions (i.e., algorithms), particularly parameters that vary for different flow setting inputs 504, may be stored in non-volatile memory.

With reference to FIG. 10, another exemplary embodiment of a product gas concentrator 10 may include an input device 12, a product gas source 14, a pressure sensor 16, a conserver valve 18, and a controller 20. In other embodiments, an in-line flow sensor 26 may be used instead of or in conjunction with the pressure sensor 16. The input device 12 may be used to select a first desired output flow rate setting for the concentrated product gas. The product gas source 14 may provide the concentrated product gas for dispensing. The pressure sensor 16 may monitor a pressure of the concentrated product gas. The conserver valve 18 may include an output connection, a vent connection, and a gas connection. The output connection may be associated with a user 22. The vent connection may be associated with a vent port 24. The gas connection may be associated with the concentrated product gas. The output connection may be switched from the vent connection to the gas connection and vice versa. The controller is in operative communication with the input device 12 and pressure sensor 16 and may selectively switch the conserver valve 18 to selectively dispense the concentrated product gas based at least in part on the selected output flow rate setting and monitored pressure. For example, the pressure sensor 16 may monitor pressure between the conserver valve 18 and the product gas source 14. In another embodiment, the pressure sensor 16 may monitor pressure in another suitable location.

In one embodiment, the controller 20 may store a first pressure value based at least in part on the corresponding monitored pressure. The controller 20 may also store a second pressure value based at least in part on the corresponding monitored pressure after the input device 12 is used to select a second desired output flow rate setting. In this embodiment, the controller 20 may determine an intermediate pressure value between the first and second pressure values based at least in part on a linear relation between the first and second pressure values and the monitored pressure.

In another embodiment, the product gas concentrator 10 may also include a flow sensor 26. The flow sensor 26 may monitor a flow indicative of a breathing cycle for the user 22. The controller 20 may be in operative communication with the flow sensor 26. For example, the flow sensor 26 may monitor flow between the conserver valve 18 and the vent port 24. In the embodiment being described, the controller 20 may determine a breathing characteristic of the user 22 based at least in part on the monitored flow. The controller 20 may selectively switch the conserver valve 18 based at least in part on the determined breathing characteristic. In other embodiments, the flow sensor 26 may monitor a flow indicative of a breathing cycle for the user 22 in other suitable locations, such as, for example, between conserver valve 18 and the user 22.

In the embodiment being described, the controller 20 may determine a start time for dispensing a bolus of concentrated product gas to the user 22 via the conserver valve 18 based at least in part on a relation between the determined breathing characteristic and a trigger threshold indicative of inhalation. The controller 20 may determine a pressure summation threshold based at least in part on the selected output flow rate setting. In the embodiment being described, the controller 20 may also determine the start time for dispensing the bolus of concentrated product gas based at least in part on expiration of a lock-out time associated with a previous bolus. The controller 20 may determine a time duration for dispensing the bolus of concentrated product gas based at least in part on a relation between the monitored pressure and the pressure summation threshold.

With reference to FIG. 11, an exemplary embodiment of a process 50 for providing a concentrated product gas may begin at 52, where a first desired output flow rate setting for the concentrated product gas may be selected. Next, a product gas source for dispensing the concentrated product gas may be provided (54). At 56, a pressure of the concentrated product gas may be monitored. Next, an output connection associated with a user may be selectively switched from a vent connection associated with a vent port to a gas connection associated with the concentrated product gas and vice versa to selectively dispense the concentrated product gas based at least in part on the selected output flow rate setting and monitored pressure (58).

In one embodiment, the process 50 may also include storing a first pressure value based at least in part on the monitored pressure, selecting a second desired output flow rate setting for the concentrated product gas, storing a second pressure value based at least in part on the monitored pressure, and determining an intermediate pressure value between the first and second pressure values based at least in part on a linear relation between the first and second pressure values.

In still another embodiment, the process 50 may also include monitoring a flow indicative of a breathing cycle for the user and determining a breathing characteristic of the user based at least in part on the monitored flow. In this embodiment, the selective switching in 58 may be based at least in part on the monitored breathing characteristic. In the embodiment being described, the process 50 may further include determining a start time for dispensing a bolus of concentrated product gas to the user via the output connection based at least in part on a relation between the monitored breathing characteristic and a trigger threshold indicative of inhalation. The process 50 may also include determining the start time for dispensing the bolus of concentrated product gas based at least in part on expiration of a lock-out time associated with a previous bolus. Additionally, in this embodiment, the process 50 may also include determining a pressure summation threshold based at least in part on the selected output flow rate setting and determining a time duration for dispensing the bolus of concentrated product gas based at least in part on a relation between the monitored pressure and the pressure summation threshold.

In the above embodiments, a VSA process is utilized to produce concentrated oxygen in combination with a pressurizing system to deliver the concentrated oxygen to the user. In this manner, the benefits of using VSA instead of PSA can be achieved, but with the effectiveness of a pressurizing system for delivery.

While the present invention has been illustrated by the description of embodiments thereof, and while the embodiments have been described in considerable detail, it is not the intention of the specification to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. For example, components that are described as being connected, affixed, or joined, can be connected, affixed or joined directly or indirectly such as through one or more intermediary components. Furthermore, sizes and geometries of various components can be changed from the various embodiments and examples shown and described herein. Therefore, the invention, in its broader aspects, is not limited to the specific details, the representative apparatus, and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of the applicant's general inventive concept. 

The invention claimed is:
 1. An apparatus for providing a concentrated product gas, comprising: first and second sieve beds arranged to separate one or more adsorbable components from a source gaseous mixture in alternating filling and purging cycles to form the concentrated product gas using a vacuum swing adsorption process; at least one product tank to store the concentrated product gas at an ambient or less than ambient pressure; a first pump arranged to deliver the concentrated product gas formed by the first and second sieve beds; and a controller to control the alternating filling and purging cycles of the vacuum swing adsorption process.
 2. The apparatus of claim 1, wherein the concentrated product gas formed by the first and second sieve beds is at the ambient or less than ambient pressure, and wherein the first pump provides the concentrated product gas at a pressure above the ambient pressure.
 3. The apparatus of claim 2, wherein the first pump comprises: a first pump inlet; and a first pump outlet; wherein the first and second sieve beds include at least one sieve bed outlet; and wherein the concentrated product gas formed by the first and second sieve beds flows from the at least one sieve bed outlet or the at least one product tank to the first pump inlet and the concentrated product gas is provided from the first pump outlet.
 4. The apparatus of claim 2, further comprising a first sensor to sense the pressure of the concentrated product gas provided by the first pump, wherein the controller further controls actuation of the first pump based at least in part on a first sensor output signal.
 5. The apparatus of claim 4, wherein the controller turns off the first pump when the first sensor output signal reaches a first predetermined value and turns on the first pump when the first sensor output signal reaches a second predetermined value.
 6. The apparatus of claim 5, wherein the first predetermined value is different than the second predetermined value.
 7. The apparatus of claim 1, further comprising an accumulator to store the concentrated product gas at a pressure above the ambient pressure.
 8. The apparatus of claim 7, further comprising a first pressure switch to sense an accumulator pressure, wherein the accumulator pressure is the pressure of the concentrated product gas stored in the accumulator, and wherein the first pressure switch controls actuation of the first pump based at least in part on the accumulator pressure.
 9. The apparatus of claim 1, wherein the first pump is further arranged to draw exhaust gas from the first and second sieve beds during the alternating filling and purging cycles.
 10. The apparatus of claim 1, further comprising a second pump arranged to draw exhaust gas from the first and second sieve beds during the alternating filling and purging cycles.
 11. The apparatus of claim 10, further comprising a pump assembly, wherein the pump assembly comprises the first pump and the second pump.
 12. The apparatus of claim 1, further comprising: an input device adapted to select a desired output setting for the concentrated product gas from a plurality of output settings; a valve assembly to selectively provide an adjustable flow between the first and second sieve beds; and wherein the controller is in operative communication with the input device and the valve assembly to selectively control the adjustable flow between the first and second sieve beds based at least in part on the desired output setting such that the flow between the first and second sieve beds for at least one output setting is different from the flow between the first and second sieve beds for at least one other output setting in relation to corresponding vacuum swing adsorption cycles.
 13. The apparatus of claim 12, wherein the valve assembly comprises a pressure equalization valve to selectively provide a second adjustable flow between the first and second sieve tanks; and wherein the controller is in operative communication with the pressure equalization valve to selectively control the pressure equalization valve.
 14. The apparatus of claim 1, wherein the controller is in operative communication with the first and second sieve beds to selectively control the alternating filling and purging cycles over a plurality of predetermined altitude ranges while maintaining an acceptable purity level for the concentrated product gas.
 15. The apparatus of claim 1, further comprising: an input device adapted to select a desired output setting for the concentrated product gas from a plurality of output settings; a pressure sensor monitoring a pressure of the concentrated product gas; and a conserver valve comprising an output connection associated with a user, a vent connection associated with a vent port, and a gas connection associated with the concentrated product gas, wherein the output connection is switched from the vent connection to the gas connection and vice versa; and wherein the controller is in operative communication with the input device and the pressure sensor to selectively switch the conserver valve to selectively dispense the concentrated product gas based at least in part on the selected output setting and the monitored pressure.
 16. The apparatus of claim 15, further comprising: a flow sensor monitoring a flow indicative of a breathing cycle for the user; wherein the controller is in operative communication with the flow sensor, determines a breathing characteristic of the user based at least in part on the monitored flow, and selectively switches the conserver valve based at least in part on the determined breathing characteristic; wherein the controller determines a start time for dispensing a bolus of concentrated product gas to the user via the output connection based at least in part on a relation between the determined breathing characteristic and a trigger threshold indicative of inhalation.
 17. The apparatus of claim 1, wherein the at least one product tank stores the concentrated product gas at a subatmospheric pressure.
 18. The apparatus of claim 1, further comprising: a sieve bed and product tank assembly, comprising: the first sieve bed; and the at least one product tank to store the concentrated product gas at an ambient or less than ambient pressure; and a sieve bed and accumulator assembly, comprising: the second sieve bed; and an accumulator to store the concentrated product gas at a pressure above the ambient pressure.
 19. An apparatus for providing a concentrated product gas, comprising: means for separating one or more adsorbable components from a source gaseous mixture in alternating filling and purging cycles to form the concentrated product gas using a vacuum swing adsorption process; means for storing the concentrated product gas at an ambient or less than ambient pressure; means for pumping to deliver the concentrated product gas formed by the means for separating one or more adsorbable components from a source gaseous mixture; and means for controlling the alternating filling and purging cycles of the vacuum swing adsorption process.
 20. A method of providing a concentrated product gas, comprising: separating one or more adsorbable components from a source gaseous mixture in alternating filling and purging cycles to form the concentrated product gas using a vacuum swing adsorption process; storing the concentrated product gas at n ambient or less than ambient pressure; and pumping the concentrated product gas formed by the vacuum swing adsorption process at a pressure above the ambient pressure. 